The invention relates to activation of a packet data protocol context when a terminal moves from one packet-switched network to another, there being no signalling interface between the networks to support mobility management.
To meet the communication needs of mobile users various public radio networks, such as a digital mobile communication system GSM (Global System for Mobile Communication), have been developed. Besides public networks with a wide coverage area, various wireless local area networks and private networks have also been developed. PMR-type (Private Mobile Radio or Professional Mobile Radio) private networks, such as TETRA (Terrestrial Trunked Radio), are typically company networks or networks for authorities, wherein all channels are used by one or more companies or authorities.
Because of the expansion of the Internet in particular, networks providing different packet-switched services have been developed in the last few years. The GPRS (General Packet Radio Service) packet radio service has been developed for packet-switched data transmission in the GSM system. The most important network elements of the GPRS are a GPRS gateway support node (GGSN) and a GPRS support node SGSN. The SGSN controls the packet data service in the area of one or more cells in a cellular-type of packet radio network. For this purpose, each support node SGSN is typically connected to a base station subsystem. A terminal in the cell communicates over the radio interface with a base station and further through the base station subsystem with the support node SGSN to whose service area the cell belongs.
The GPRS gateway support node GGSN communicates with external networks, i.e. combines the GPRS service of the operator with other packet networks, such as an IP-based network (e.g. Internet, Intranet) or an X.25 network. The GGSN comprises routing information, i.e. SGSN addresses, of GPRS subscribers and external network addresses relating to packet data protocol contexts (PDP). The GGSN functions as a router between an external address and internal routing information (e.g. SGSN). The GGSN can also transmit packets from one mobile station to another inside the network.
A mobile station attached to the GPRS can receive and/or transmit data packets on the basis of a certain PDP address, provided that the corresponding PDP (Packet Data Protocol) context is activated in the mobile station, the serving support node and the GGSN. When a connection to external networks needs to be established, the gateway support node (GGSN) to be used is selected on the basis of an access point name APN. The connection to the external networks is arranged through the access point, and the GGSN address can be defined on the basis of the access point name APN. The serving GPRS support node SGSN transmits a ‘Create PDP Context Request’ to the GGSN, which is selected according to the GGSN address stored in the subscriber data or according to the access point name given by the mobile station, or to the default GGSN which is known by the SGSN. The PDP context activation makes the mobile station known to the corresponding GGSN, and the co-operation with the external data networks may begin. A tunnel is thereby formed between the gateway support node GGSN and the support node SGSN serving the mobile station. The tunnel can be formed by utilizing a GPRS tunnelling protocol GTP between the SGSN and the GGSN, the protocol being defined in the GPRS specification GSM 09-60 “GPRS Tunneling Protocol (GTP) across the Gn and Gp Interface”, version 6.2.0, October 1998.
When a subscriber moves from one support node to be served by another support node, the PDP context routing information of the GGSN is updated by using the address of the new support node. When the support nodes and the gateway support nodes belong to the same GPRS network (the same PLMN, Public Land Mobile Network), the interface between them is Gn. If the subscriber moves to a new GPRS network (the PLMN is different), the new support node can request the old support node for the PDP context information and it can update the PDP context information in the GGSN via the interface Gp.
The GGSN can be used as a gateway support node to the external networks also for other nodes than the SGSN support node, as is illustrated in FIG. 1. In principle, any packet-switched network NW1, NW2 can establish a connection to the GGSN by using the GTP tunnelling protocol according to the GPRS standard. The GGSN can function as a gateway support node to other packet networks PDN (1) for the home network NW1 of the subscriber using the mobile station MS. A home network refers to a network in which all subscriber data relating to a mobile station MS subscriber and required in the network are maintained permanently, which means that a home location register is to be found in the home network. In such a case, a packet data protocol context is activated between the mobile station MS, the home network NW1 and the GGSN. The interface Gn of the GPRS system can be used between the network NW1 and the GGSN. When the context is activated, data can be transferred between the mobile station and the external packet networks PDN. When the subscriber moves in the network NW1 area, the information on the PDP context changes is transmitted, if required, (if the support node serving the mobile station of the network NW1 changes) to the GGSN.
When the mobile station MS moves to the coverage area (2) of a base station of the visited network NW2, the mobile station MS roams the network NW2. In some cases there is no signalling interface between the different packet radio networks to support the mobility. Between various private networks in particular there is typically no signalling interface that is required, nor do they thus support roaming. If there is no signalling interface and the mobile station MS tries to request for a service in the network NW2 area, the visited network NW2 does not obtain any information relating to the subscriber or the PDP context activated in the network NW1 from the home network NW1.
The problem is in particular that the visited network does not obtain information on the gateway support node GGSN to be used, and the packet data protocol context cannot thus be activated through the visited network to the gateway support node. If the access point name is transmitted from the mobile station, the visited network cannot limit the selection of the access point (and of the gateway support node) in a manner required by the home network.